An oil change interval for a vehicle may provide an indication of distance or duration of vehicle operation until next oil change. The oil change interval may be based on degradation of engine oil, which may occur due to one or more factors including fuel dilution of engine oil. For example, during cold engine operation, if the engine does not reach stable engine operating conditions, fuel dilution of the engine oil can occur. For example, fuel may mix with engine oil in an engine's crankcase. Repeated cold start engine operation without completing engine warm-up may result in excessive fuel dilution and degradation of oil quality. Further, the engine may be operated with late fuel injection timing in order to reduce particulate matter emissions, which may increase oil dilution, especially during repeated cold engine starts before the engine has warmed up. Further still, in vehicle systems equipped with a diesel particulate filter (DPF), post fuel injections may be performed to increase an exhaust temperature for regeneration of the DPF. During post fuel injections, some of the post-injected fuel may deposit onto the cylinder wall and drain into an oil pan, which may increase fuel dilution of the engine oil.
However, fuel dilution of engine oil may vary based on the driving style. For example, highway driving may facilitate evaporation of lighter fraction of fuel in oil, thereby decreasing fuel dilution of engine oil. The variations in fuel dilution of engine oil may cause significant variations in the oil change interval, which is less desirable, in particular, when the oil change interval is displayed to a customer. Further, based on the oil dilution amount one or more adjustments to engine operating conditions, such as increasing engine temperature and injecting fuel early, may be performed to mitigate oil dilution. Thus, a transient increase in oil dilution amount may cause an engine controller to take unnecessary actions to mitigate oil dilution, which may influence fuel economy and emissions. For example, increasing engine temperature may reduce fuel economy and adapting early fuel injection timings may increase particulate emissions. On the other hand, a transient decrease in oil dilution amount may increase the oil change interval and thus, cause a delay in informing the customer regarding the need to change oil immediately.
In one example, the issues described above may be addressed by a method for a vehicle engine, comprising: determining a filtered oil dilution amount by filtering an estimated oil dilution amount of an engine oil; and indicating oil degradation based on the filtered oil dilution amount; wherein an amount of filtering is adjusted based on the estimated oil dilution amount. In this way, the estimated oil dilution data may be filtered based on the estimated oil dilution. Specifically, the filtering may be adjusted to filter out transient dynamics at lower dilutions while increasing sensitivity to variations at higher dilutions.
In one example, when the estimated oil dilution amount is less than a threshold amount, a larger time constant may be implemented for the filter; otherwise, a smaller time constant may be implemented. Further, a current service interval (that is distance and/or time remaining until next oil change) may be determined based on the filtered oil dilution amount. Further, responsive to the filtered output increasing above a higher threshold, an indication may be provided to a user to change oil. By choosing the larger time constant, transient dynamics in oil dilution amounts may be filtered out at lower oil dilution. Therefore, the current service interval is displayed to the user, transient degradation dynamics are filtered out. However, when the estimated oil dilution amount is at or greater than the threshold, by choosing a smaller time constant, the filtered output may closely follow changes in the oil dilution amount. The smaller time constant increases the sensitivity of the filter and improves a filter response time. Therefore, latency in delivering the filtered output is reduced and the user may be informed of the need to change oil in a timely manner when the filtered output reaches the higher threshold dilution.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.